Oil system and a generator including such an oil system

ABSTRACT

An oil system is provided having a first inlet ( 20 ) for receiving oil from a fist source, such as a generator, and a second inlet ( 32 ) for receiving oil from other oil systems. A scavenge pump ( 14 ) has a manifold ( 26 ) arranged such that oil is preferentially pumped from the first inlet.

FIELD OF THE INVENTION

[0001] The present invention relates to an oil system, and in particular to the configuration of the scavenge pump and associated oil feeds.

BACKGROUND OF THE INVENTION

[0002] A fluid, such as oil, may be used for multiple tasks within an item of machinery. In the context of an aeronautical generator, oil may be used to cool the generator, to lubricate the generator, to lubricate drive components associated with the generator and to act as hydraulic control fluid within a control system associated with the generator. The applicant has co-pending patent applications for a constant frequency aeronautical generator system in which a variable input shaft speed is converted to a substantially constant output speed by a continuously variable transmission incorporating a segmented belt extending between two variable diameter pulleys. The pulleys comprise opposed relatively moveable flanges having inclined surfaces such that the surfaces become progressively further apart with increased radial distance from the axis of rotation of the pulley. Thus, by controlling the separation between the two pulleys, a belt of fixed width may be forced to undergo motion around the pulley at a radius controlled by the separation of the relatively moveable flanges. In order to control the position of the flanges, and the pressure that they exert on the belt interposed between them, oil at high pressure, ducted by various control valves, is used as an hydraulic control fluid.

[0003] Under normal operating conditions, the flow rates of oil from the generator, from the variable pulley control valves, and various cooling flows of oil can be calculated. Indeed, under all “normal” flight conditions the various flow rates generally lie within well defined bands. After the oil has been used for its intended purpose, it is normally ducted to a collection point, for example in a sump, where the oil is recovered by a scavenge pump such that it can be re-circulated.

[0004] For a complex item of machinery, such as an aeronautical generator, weight and performance are critical issues. Thus every component selection has to be a compromise between performance and overall generator weight. This is especially true where the component is required to be retrofittable into existing aircraft designs and must conform to pre-existing space and weight limits in order to avoid the need for the aircraft to be re-certified for flight using such a component. It therefore is normal practice that the scavenge pump is selected to be as small and light as reasonably possible and consequently the maximum scavenge pump flow rate is generally closely matched to the normal oil flow rate, adjusted by an appropriate safety margin.

[0005] Aircraft, both military and civilian, may experience moments of low or negative G. In civilian aircraft, this may occur as a result of air turbulence. Such low or negative G conditions may perturb the return of oil from various generator components to the sump and scavenge pump. This may result in the rate of return of oil being reduced for a period of several seconds. However, many or all of the generator sub systems may continue to use oil at their normal rate and consequently once the low or zero G condition no longer exists the amount of oil to be scavenged from the sump may be in excess of the scavenge pump's capacity and a pumping “backlog” may exist for a period of time.

[0006] The generator cannot survive having excess oil in it for any prolonged period of time. The accumulation of oil in the generator will quickly result in overheating and give rise to the possibility of damage occurring within the generator.

SUMMARY OF THE INVENTION

[0007] According to a first aspect of the present invention, there is provided an oil system comprising a first fluid inlet for receiving fluid from a first source, a second fluid inlet for receiving fluid from a second source, and a pump, wherein a pump inlet is configured to preferentially accept fluid from the first inlet.

[0008] It is thus possible to provide an oil system wherein returns of oil from various components within a machine are pumped according to different priorities. Thus, in the context of an aeronautical generator system, oil is preferentially removed from the vicinity of the generator. Preferably the second fluid inlet is associated with a reservoir region such that fluid that would have been accepted via the second fluid inlet can temporarily reside in the reservoir region. The reservoir region may, for example, be the sump of a machine. Thus oil could temporarily reside in the sump whilst the scavenge pump clears the pumping backlog.

[0009] Oil from the generator is normally removed via a plurality of generator drains. These may advantageously be in communication with a first duct which is in direct fluid flow communication with the inlet of the pump. Thus, rather than having the generator drain into the sump, the duct from the generator drains is in direct or substantially direct connection with the pump.

[0010] In an embodiment of the present invention, the pump is provided with an inlet manifold which terminates in a pipe which extends within, or at least closely faces, the generator outlet duct. In an alternative arrangement, the generator outlet duct and the inlet manifold may be of the same size, and indeed may be joined so as to effectively form a single component, with one or more apertures formed within the periphery in order to act as the second inlet. Flow deflection means, such as internal plates or distortion of the wall of the structure may be provided in order to direct the flow of fluid from the generator such that, under normal operating conditions, it does not exit through the apertures except, possibly under conditions where the scavenge pump is unable to handle the flow rate.

[0011] Advantageously the second fluid input is used to receive oil return from systems which have a low drainage priority, such as lubrication oil.

[0012] Advantageously a third fluid input is provided to receive fluid from the output of a further device or system. The further device may be a control valve of a hydraulic control system. The outlet of the control valve may be arranged to drain into the reservoir region. However, it may be desirable that the output of the control valve is given greater pumping priority than the fluid admitted via the second inlet. In which case the pump inlet may be arranged to accept fluid from the third inlet in preference to fluid from the second inlet. Thus the third inlet may join the pump inlet manifold by a direct connection.

[0013] It is possible that the operation of a control valve connected to a third inlet may be perturbed by negative pressures occurring at the outlet of the control valve and as a result of operation of the scavenge pump. In order to overcome this, advantageously an air intake valve may be in fluid flow communication with the outlet of the control valve. The air intake valve may be arranged to admit air into the scavenge pump inlet manifold. The air may preferentially be admitted from within the casing of the machine, with a second option to admit air from the exterior of the machine should the internal pressure within the machine become too low. Aeronautical generators are frequently operated at an over pressure, so air would only be admitted from the exterior of the generator once the air pressure within the generator falls below the ambient pressure.

[0014] It is thus possible to provide a generator configuration which preferentially removes oil from components which are sensitive to the presence of the excess oil, and which also allows for control of pressurisation of the case of the machine without the need for a separate pumping mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will further be described, by way of example, with reference to the accompanying drawings, in which:

[0016]FIG. 1 schematically illustrates the components within an aeronautical generator having an oil system constituting an embodiment of the present invention;

[0017]FIG. 2 schematically represents the connections to a pump inlet manifold in an oil system constituting an embodiment of the present invention; and

[0018]FIG. 3 schematically illustrates an embodiment of the present invention using flow deflectors.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0019]FIG. 1 schematically illustrates an oil system within an aeronautical generator. The oil system comprises a de-aerator 2 which in effect acts as a reservoir of oil. Oil from the de-aerator is provided to one or more pumps 4 (which may be both high pressure pumps and low pressure pumps) which then provide oil to cool and lubricate a generator 6, to provide pressurised working fluid for operation of control systems 8 and to act as a lubricant for gears and bearings, as indicated schematically by box 10. Oil return paths lead from each of the systems 6, 8 and 10 towards a sump 12 where the oil collects prior to being pumped from the sump by a scavenge pump 14 which returns the oil, after suitable filtering and cooling to the de-aerator 2.

[0020]FIG. 2 shows the configuration of the inlet to the scavenge pump 14 more clearly. Oil from the generator is initially dusted towards a generator outlet duct 20 which conveys oil from the generator towards the sump 12. An outlet 22 of the generator outlet duct 20 is provided adjacent but above the floor 24 of the sump 12. A scavenge pump inlet manifold 26 extends from the inlet of the scavenge pump 14 and terminates at an end portion 28 adjacent the floor 24 of the sump 12 and extending into the interior of the generator outlet duct 20. Thus oil flowing along the generator outlet duct 20 is primarily directed into the interior of the inlet manifold 26. A gap 30 exists between the interior of the generator outlet duct 20 and the end portion 28 of the inlet manifold 26. This gap allows fluid communication between oil contained in the sump 12 and the inlet manifold 26. Oil that has been used for lubrication also collects in the sump 12, for example by being ducted along a further pipe 32, from where the oil can be removed from the sump by virtue of the reduced pressure within the inlet manifold 26. Thus, in use, the sump serves to act as a reservoir for oil that is to be removed by the scavenge pump. In the event of a low, zero or negative G situation, oil will move away from the bottom of the sump and consequently away from the inlet portion 28 of the scavenge pump inlet manifold 26. However oil will still issue from the control system 8 and from the lubrication system 10. When normal gravity returns, oil will again flow into the sump. However, because removal of oil from the sump has been temporarily suspended there will be excess oil in the sump and the oil return system will “backup”. It will therefore take some time for the scavenge pump to remove the excess oil.

[0021] The oil supply to the generator 6 is generally configured that the supply will be inhibited during low gravity or inverted conditions. However, once normal G conditions are resumed, oil supply will be resumed to the generator. Thus oil flowing from the generator will then flow out along the duct 20. Oil in this duct receives preferential pumping treatment in order to ensure that oil does not accumulate within the generator.

[0022] A control valve 40 for the control systems 8 and other associated control components also requires oil to be removed therefrom for re-circulation. The control valve 40 has an outlet duct 42 which connects directly to the inlet manifold 26 at an intermediate portion thereof. This connection arrangement provides an assurance that oil will be sucked away from the outlet of the control valve 40, even under low, zero or negative G or inverted conditions by virtue of the reduced pressure within the manifold 26. However, some control valve configurations are sensitive to excess negative pressure at the outlet thereof. Thus, in effect, the control valve will not tolerate having oil sucked out of it by the scavenge pump. In order to overcome this problem, an air introduction means 44 is provided intermediate the outlet of the control valve 40 and the inlet of the scavenge pump 14. An air duct 46 extends from a position between the outlet of the control valve 40 and the inlet of the scavenge pump 14 to a air control valve 48. The air control valve has a first inlet 50 which is in gas flow communication with the interior of a casing surrounding the machine and a second inlet 52 which is in gas flow communication with the atmosphere surrounding the machine. In general, the generator is arranged to have a excess pressure within its casing. Thus provided the excess pressure exist any tendency to suck oil out of the outlet of the control valve 40 will cause air from the interior of the casing to be admitted via the first inlet 50 and to be ducted into the inlet pipe 42 via the duct 46. However, should the air pressure within the generator drop below the local atmospheric pressure air may then be admitted via the second inlet 52. Thus this arrangement serves to pressurise the interior of the generator to a normal working pressure without requiring the provision of a separate pump.

[0023]FIG. 3 shows an alternative arrangement in which the outlet duct 20 blends or merges with the inlet manifold 26 so as to form an uninterrupted path from the generator to the scavenge pump. An aperture 60 (which may be one of several) is formed in the side-wall of the outlet duct 20 or inlet manifold 26 such that the aperture is at an appropriate drain/scavenge level within the sump 12. A deflector 62 is provided so as to deflect the flow of oil from the generator, thereby reducing or stopping leakage of oil from the interior of the outlet duct 20 into the sump 12. The deflector may be formed by distoring the wall of the outlet duct in the vicinity of the aperture.

[0024] It is thus possible to provide an arrangement in which, following unusual operating conditions, a scavenge pump recommences operation by removing oil from those components which are most at risk from adverse effects of excessive oil. The configuration of components also means that the scavenge pump, which by its very nature is able to handle mixed phase (liquid and gas) pumping serves not only to scavenge oil and to return it to the oil system, but also acts to control air pressure within the casing of the machine by allowing air to be omitted when the internal pressure drops below atmospheric pressure. 

1. An oil system comprising a first fluid inlet for receiving fluid from a firs source, a second fluid inlet for receiving fluid from a second source, and a pump, wherein a pump inlet is configured to preferentially accept fluid from the fist inlet.
 2. An oil system as claimed in claim 1, wherein returns of oil from various components within a machine serviced by the oil system are pumped according to respective priorities.
 3. An oil system as claimed in claim 1, wherein the second fluid inlet is associated with a reservoir region such that fluid can temporarily reside in the reservoir region.
 4. An oil system as claimed in claim 1, wherein the oil system is associated with an aeronautical generator, and oil is preferentially pumped from the vicinity of the generator.
 5. An oil system as claimed in claim 4, wherein oil removed from the generator passes along a first duct which is in direct or in substantially direct fluid flow communication with the pump inlet.
 6. An oil system claimed in claim 5, in which the pump is provided with an inlet manifold which terminates in a pipe which extends within the fist duct or closely faces the first duct.
 7. An oil system as claimed in claim 5, in which the pump is provided with an inlet manifold which has a region substantially the same size or integrally formed with the first duct, and at least one aperture is provided in one of the first duct and the inlet manifold in order to form the second inlet.
 8. An oil system as claimed in claim 7, in which flow deflectors are provided such that fluid does not exit from the at least one aperture under normal operating conditions.
 9. An oil system as claimed in claim 4, in which the second input receives oil returned from systems which have a low drainage priority.
 10. An oil system as claimed in claim 4, in which a third input is provided to receive fluid from a further device or system.
 11. An oil system as claimed in claim 10, wherein the further device is a control valve of a hydraulic control system, and wherein greater pumping priority is given to the third inlet than is given to the second inlet.
 12. An oil system as claimed in claim 11, in which an air inlet valve is in fluid flow communication with an outlet of the control valve, and wherein the air inlet valve operates to admit air in the event that the pressure at the outlet of the control valve drops to below a predetermined pressure.
 13. An oil system as claimed in claim 12, in which the air inlet valve opens to prevent negative pressure of sufficient magnitude occurring at the outlet of the control valve whereby operation of the valve may be perturbed.
 14. An oil system as claimed in claim 12, whereby the air inlet valve admits air from the exterior of the generator.
 15. A generator system having an oil system, wherein the oil system comprises a first fluid inlet for receiving oil from the generator, and a second fluid inlet for receiving the oil from an oil return path, and a pump, wherein the pump is configured to preferentially accept oil from the generator. 